Formula 1's next engine regulations are set to introduce V8 turbo hybrid engines that are simplified and made less expensive compared to the existing rules.
A proposal document sent by governing body the FIA to the six manufacturers in F1 outlines a framework for discussions on engines to be introduced in either 2030 or 2031.
Multiple sources within F1 have provided BBC Sport with the details within the document.
The plan, which comes after initial discussions with individual engine manufacturers on a one-to-one basis, proposes cheaper, lighter, simpler engines with a more visceral sound.
However, the FIA has moved away from its initial proposal to return to naturally aspirated engines.
The stated aim of the new rules is to introduce lighter, more responsive cars, increased emphasis on driver skill, relevant technologies, reduced cost, to make it easier for new manufacturers to enter F1 and to continue with the sport's commitment to reducing emissions.
This comes after criticism of the new engines introduced this year for their complexity and the way their design and operation has diminished the driving challenge of some of F1's best corners.
The engines used in F1 at the moment are 1.6-litre V6 turbos with a power split of 53-47 between the internal combustion engine and electrical components. This will be changed to 60-40 in two steps by 2028.
The FIA document proposes a V8 engine with a capacity of between 2-2.3-litres with a smaller turbo running at reduced boost pressure and a less powerful hybrid system.
The electrical motor would have a recovery capacity of 200kW compared to the current 350kW.
The idea is for 100kW (134bhp) of this to be available at all times, with a further 100kW to be used for a push-to-pass or overtake mode.
The rest of the total power output of in the region of 900bhp will be provided by the internal combustion engine.
F1 will continue with fully sustainable fuels but with the ambition to make the requirements around them less complex and therefore much cheaper to produce.
The aim is to cut a total of 80kg from the overall weight of the cars.
The proposal changes the previous stance of the FIA on naturally aspirated engines - FIA president Mohammed Ben Sulayem initially proposed a return of V10s at the start of last year and has more recently been pushing V8s.
The addition of the turbo satisfies the need for the engines to be road-relevant, as well as increasing efficiency and requiring less fuel than a pure naturally aspirated engine.
The published proposals can be seen as a kind of middle ground between Ben Sulayem's initial stance, the desire of at least some manufacturers to keep turbos and a significant hybrid element, and a recognition that the latest rules were flawed in concept and execution.
The new engines will have none of the problems of energy starvation about which drivers have complained this season.
Fernando Alonso has called F1 the "battery world championship" and described fast corners as "the charging station for the car", while Max Verstappen has called the new rules "Formula E on steroids" and anti-racing.
Both have since tempered their criticisms having seen that the sport's bosses have listened to their comments on the engines and made immediate changes to the rules this year as well as started working towards a new direction in the future.
The fundamental framework of the proposal for the new engine's architecture is said to be basically acceptable to all the manufacturers.
However, the details around the fundamentals of how the rules operate will need discussion.
The document outlines two possible ways forward for the new rule set.
One is aimed at minimising necessary adaptation - for example, a 2.1-litre V8 could be produced by simply adding two cylinders to the current 1.6-litre blocks and reducing the size of the turbo and MGU-K (hybrid motor).
The other, more controversial, is to have an external manufacturer design and supply a baseline power-unit with a high degree of standardisation, on to which manufacturers could add a degree of customisation.
However, insiders says the manufacturers are all aligned on wanting to design and build their own power-units and for engines to remain a performance differentiator.
The companies who currently supply engines to F1 teams are Mercedes, Ferrari, Audi, Honda and Red Bull. Cadillac, which entered F1 this year with its own team, is planning to produce an engine to the new rules.
There are two further arguments to steer away from the standardisation route:
The first is that the reasons for it - to safeguard against manufacturers leaving the sport - is irrelevant as all six will be committed under the new rule set.
The second is that the standardisation of electronics control units this season has led to a series of problems, such as at the start of the Bahrain Grand Prix in Malaysia when cars were restricted to not much more than walking pace because of a software bug.
The document outlines a proposal to cut the engine budget cap by 50% from the current level of $190m (£143m) per year.
However, this is considered a starting point for discussions, while there are also concerns about providing a suitable glide path down to the new number to enable teams to manage the impact on workforces.
Discussions around the budget cap also involve the need to balance ongoing development of the existing engines with design and construction of the new ones.
That topic is interlinked with whether the new rules will come into force in 2030 or 2031.
The existing contracts in F1 bind the FIA, teams and commercial rights holder together only until 2030.
Ben Sulayem has previously threatened to introduce his own rules unilaterally in 2031.
That threat appears to have receded and the process has been marked by a spirit of co-operation, which is expected to continue.
An FIA spokesperson declined to comment on or discuss the document, pointing instead to an Instagram post published on Ben Sulayem's account outlining the aims and objectives of of the new rules. It makes no mention of turbos or hybrid technology.
The aim is for discussions over the next weeks to lead to a proposal that can be put to F1's legislative body, the FIA world council, in December.
